The present invention relates generally to the alignment of an acetabular implant device in connection with the implantation of a prosthetic hip joint in a natural pelvis and pertains, more specifically, to an apparatus and method which utilizes a disposable trial impingement sensor to guide the appropriate alignment of the acetabular device at an implant site in the pelvis.
Many articulating joints of the body, such as the joints of the hips, have anatomical ball and socket connections between bones of the joints providing a wide range of motion. The hip joint, for instance, includes a socket or acetabulum in the pelvis and a femoral head or ball at an upper end of the femur or thigh bone received in the acetabulum. Where natural articulating joints are congenitally defective or become degraded due to disease or injury, prosthetic or artificial ball and socket components are commonly implanted in the body to replace the natural ball and socket structure of the joints. In total joint replacement surgery, prosthetic ball and socket components are both implanted as, for example, in total hip arthroplasty wherein a femoral stem component having a head or ball thereon to replace the natural femoral head is affixed to the femur. A socket or acetabular component having an outer shell member and a bearing insert or liner received in a cavity of the shell is affixed to the acetabulum. The head or ball of the femoral component is rotatably or pivotally received in a socket of the liner to recreate the natural articulation of the hip joint. In subtotal or partial joint replacement surgery, natural bone structure of the joint is left intact to cooperate with an implanted prosthetic component. One example of subtotal joint replacement surgery being a cup arthroplasty wherein a prosthetic acetabular or socket component is implanted in the acetabulum to receive the natural femoral head.
It is extremely important in total or partial joint replacement surgery and, in particular, total and subtotal hip replacement surgery, that the ball and socket components be optimally positioned in accordance with the physiological and anatomical features of the patient to ensure implant stability, resist dislocation and subluxation of the joint, enhance range of motion and avoid loosening or failure of the components. Accordingly, the liners of prosthetic acetabular components employed in hip surgery have been designed to protrude beyond openings to the cavities of the shells to angularly position the sockets of the liners to provide optimal coverage of the prosthetic femoral heads by the socket components to resist dislocation. Many acetabular components including liners having socket openings therein and shells or cups having cavities therein with openings for receiving the liners with portions of the liners angularly protruding beyond the planes of the cavity openings to angularly position the socket openings to receive a head or ball. The portions of the liners protruding beyond the planes of the cavity openings define angularly protruding lips or overhangs and, in some prosthetic socket components, the liners can be rotated relative to the shells about axes perpendicular to the planes of the cavity openings to change the position of the lips or overhangs to inhibit dislocation.
Currently available acetabular alignment apparatus and procedures generally rely upon either the use of reference locations external to the pelvis of a patient, or direct observation of an implant site by a surgeon during a prosthetic hip joint implant procedure. The reliance upon external references tends to introduce inaccuracies arising from variations in a patient's position on the operating room table. Thus, despite the use of elaborate and expensive equipment in connection with such procedures, reliable and consistent results are not assured. On the other hand, while alignment guides used by surgeons in connection with direct observation techniques are relatively simple and inexpensive, and can expedite the implant procedure, accuracy of alignment depends heavily upon the skill of the surgeon and can vary widely among practitioners in the field.
The instrument of U.S. Pat. No. 6,395,005 provides an alignment apparatus and method which rely upon specific anatomic structures available internally at the pelvis to furnish natural landmarks as references for attaining accurate alignment of an acetabular device at an implant site in the pelvis. However, it is still difficult for the surgeon to position the acetabular to prevent dislocation due to impingement between the femoral component and the acetabular cup.